Infective and inactivated filamentous phage as carriers for immunogenic peptides

Bacteriophage M13KE as a nanoparticle platform to display and deliver a pathogenic epitope: Development of an effective porcine epidemic diarrhoea virus vaccine

Porcine epidemic diarrhoea virus (PEDV) is a porcine enteric coronavirus, outbreaks and epidemics of which have caused huge economic losses to the livestock industry. The disadvantage of existing PEDV vaccines is that the unstable efficacy and high cost limit their widespread use. Therefore, there is an urgent need to develop a recombinant transgenic vaccine candidate for PEDV. In this study, three linear epitopes on the PEDV spike (S) were screened using peptide scanning. The screened epitopes were linked to targeting peptides for lung and intestinal epithelial cells, respectively, and displayed on the M13KE phage to form recombinant phage nanoparticles. Active immunisation experiments showed that a single B-cell epitope delivered by M13KE phage nanoparticles induced the production of specific neutralising antibodies against PEDV in mice. After PEDV stimulation, the immunised mice had significantly higher levels of interferon-γ (IFN-γ) than the control group. Simultaneously, PEDV stimulation caused lymphocyte activation and proliferation in the immunised mice, which is a typical immune response to viral infections. These results suggest that a single linear antigenic epitope delivered by M13KE phage nanoparticles induces significant humoral and cellular immune responses. The constructed recombinant phage nanoparticles are expected to be potential vaccine candidates for PEDV.

Designing a multi-epitope influenza vaccine: an immunoinformatics approach

Influenza continues to be one of the top public health problems since it creates annual epidemics and can start a worldwide pandemic. The virus's rapid evolution allows the virus to evade the host defense, and then seasonal vaccines need to be reformulated nearly annually. However, it takes almost half a year for the influenza vaccine to become accessible. This delay is especially concerning in the event of a pandemic breakout. By producing the vaccine through reverse vaccinology and phage display vaccines, this time can be reduced. In this study, epitopes of B lymphocytes, cytotoxic T lymphocytes, and helper T lymphocytes of HA, NA, NP, and M2 proteins from two strains of Influenza A were anticipated. We found two proper epitopes (ASFIYNGRL and LHLILWITDRLFFKC) in Influenza virus proteins for CTL and HTL cells, respectively. Optimal epitopes and linkers in silico were cloned into the N-terminal end of M13 protein III (pIII) to create a multi-epitope-pIII construct, i.e., phage display vaccine. Also, prediction of tertiary structure, molecular docking, molecular dynamics simulation, and immune simulation were performed and showed that the designed multi-epitope vaccine can bind to the receptors and stimulate the immune system response.

The Combination of Antibiotic and Non-Antibiotic Compounds Improves Antibiotic Efficacy against Multidrug-Resistant Bacteria

Bacterial antibiotic resistance, especially the emergence of multidrug-resistant (MDR) strains, urgently requires the development of effective treatment strategies. It is always of interest to delve into the mechanisms of resistance to current antibiotics and target them to promote the efficacy of existing antibiotics. In recent years, non-antibiotic compounds have played an important auxiliary role in improving the efficacy of antibiotics and promoting the treatment of drug-resistant bacteria. The combination of non-antibiotic compounds with antibiotics is considered a promising strategy against MDR bacteria. In this review, we first briefly summarize the main resistance mechanisms of current antibiotics. In addition, we propose several strategies to enhance antibiotic action based on resistance mechanisms. Then, the research progress of non-antibiotic compounds that can promote antibiotic-resistant bacteria through different mechanisms in recent years is also summarized. Finally, the development prospects and challenges of these non-antibiotic compounds in combination with antibiotics are discussed.

Phage based vaccine: A novel strategy in prevention and treatment

The vaccine was first developed in 1796 by a British physician, Edward Jenner, against the smallpox virus. This invention revolutionized medical science and saved lives around the world. The production of effective vaccines requires dominant immune epitopes to elicit a robust immune response. Thus, applying bacteriophages has attracted the attention of many researchers because of their advantages in vaccine design and development. Bacteriophages are not infectious to humans and are unlikely to bind to cellular receptors and activate signaling pathways. Phages could activate both cellular and humoral immunity, which is another goal of an effective vaccine design. Also, phages act as an effective adjuvant, along with the antigens, and induce a robust immune response. Phage-based vaccines can also be administered orally because of their stability in the gastrointestinal tract, in contrast to common vaccination routes, which are intradermal, subcutaneous, or intramuscular. This review presents the current improvements in phage-based vaccines and their applications as preventive or therapeutic vaccines.

Improving the safety and efficacy of phage therapy from the perspective of phage-mammal interactions

Phage therapy has re-emerged as a promising solution for combating antimicrobial-resistant bacterial infections. Increasingly, studies have revealed that phages possess therapeutic potential beyond their antimicrobial properties, including regulating the gut microbiome and maintain intestinal homeostasis, as a novel nanocarrier for targeted drug delivery. However, the complexity and unpredictability of phage behavior during treatment pose a significant challenge in clinical practice. The intricate interactions established between phages, humans, and bacteria throughout their long coexistence in the natural ecosystem contribute to the complexity of phage behavior in therapy, raising concerns about their efficacy and safety as therapeutic agents. Revealing the mechanisms by which phages interact with the human body will provide a theoretical basis for increased application of promising phage therapy. In this review, we provide a comprehensive summary of phage-mammal interactions, including signaling pathways, adaptive immunity responses, and phage-mediated anti-inflammatory responses. Then, from the perspective of phage-mammalian immune system interactions, we present the first systematic overview of the factors affecting phage therapy, such as the mode of administration, the physiological status of the patient, and the biological properties of the phage, to offer new insights into phage therapy for various human diseases.

The Breadth of Bacteriophages Contributing to the Development of the Phage-Based Vaccines for COVID-19: An Ideal Platform to Design the Multiplex Vaccine

Phages are highly ubiquitous biological agents, which means they are ideal tools for molecular biology and recombinant DNA technology. The development of a phage display technology was a turning point in the design of phage-based vaccines. Phages are now recognized as universal adjuvant-free nanovaccine platforms. Phages are well-suited for vaccine design owing to their high stability in harsh conditions and simple and inexpensive large-scale production. The aim of this review is to summarize the overall breadth of the antiviral therapeutic perspective of phages contributing to the development of phage-based vaccines for COVID-19. We show that phage vaccines induce a strong and specific humoral response by targeted phage particles carrying the epitopes of SARS-CoV-2. Further, the engineering of the T4 bacteriophage by CRISPR (clustered regularly interspaced short palindromic repeats) presents phage vaccines as a valuable platform with potential capabilities of genetic plasticity, intrinsic immunogenicity, and stability.

A combination therapy of Phages and Antibiotics: Two is better than one

Emergence of antibiotic resistance presents a major setback to global health, and shortage of antibiotic pipelines has created an urgent need for development of alternative therapeutic strategies. Bacteriophage (phage) therapy is considered as a potential approach for treatment of the increasing number of antibiotic-resistant pathogens. Phage-antibiotic synergy (PAS) refers to sublethal concentrations of certain antibiotics that enhance release of progeny phages from bacterial cells. A combination of phages and antibiotics is a promising strategy to reduce the dose of antibiotics and the development of antibiotic resistance during treatment. In this review, we highlight the state-of-the-art advancements of PAS studies, including the analysis of bacterial-killing enhancement, bacterial resistance reduction, and anti-biofilm effect, at both in vitro and in vivo levels. A comprehensive review of the genetic and molecular mechanisms of phage antibiotic synergy is provided, and synthetic biology approaches used to engineer phages, and design novel therapies and diagnostic tools are discussed. In addition, the role of engineered phages in reducing pathogenicity of bacteria is explored.

Bacteriophages as Therapeutic and Diagnostic Vehicles in Cancer

Evolution of nanomedicine is the re-design of synthetic and biological carriers to implement novel theranostic platforms. In recent years, bacteriophage research favors this process, which has opened up new roads in drug and gene delivery studies. By displaying antibodies, peptides, or proteins on the surface of different bacteriophages through the phage display technique, it is now possible to unravel specific molecular determinants of both cancer cells and tumor-associated microenvironmental molecules. Downstream applications are manifold, with peptides being employed most of the times to functionalize drug carriers and improve their therapeutic index. Bacteriophages themselves were proven, in this scenario, to be good carriers for imaging molecules and therapeutics as well. Moreover, manipulation of their genetic material to stably vehiculate suicide genes within cancer cells substantially changed perspectives in gene therapy. In this review, we provide examples of how amenable phages can be used as anticancer agents, especially because their systemic administration is possible. We also provide some insights into how their immunogenic profile can be modulated and exploited in immuno-oncology for vaccine production.

Bacteriophage-Based Vaccines: A Potent Approach for Antigen Delivery

Vaccines are considered one of the most important bioproducts in medicine. Since the development of the smallpox vaccine in 1796, several types of vaccines for many diseases have been created. However, some vaccines have shown limitations as high cost and low immune responses. In that regard, bacteriophages have been proposed as an attractive alternative for the development of more cost-effective vaccines. Phage-displayed vaccines consists in the expression of antigens on the phage surface. This approach takes advantage of inherent properties of these particles such as their adjuvant capacity, economic production and high stability, among others. To date, three types of phage-based vaccines have been developed: phage-displayed, phage DNA and hybrid phage-DNA vaccines. Typically, phage display technology has been used for the identification of new and protective epitopes, mimotopes and antigens. In this context, phage particles represent a versatile, effective and promising alternative for the development of more effective vaccine delivery systems which should be highly exploited in the future. This review describes current advances in the development of bacteriophage-based vaccines, with special attention to vaccine delivery strategies. Moreover, the immunological aspects of phage-based vaccines, as well as the applications of phage display for vaccine development, are explored. Finally, important challenges and the future of phage-bases vaccines are discussed.

Mimotope-based antigens as potential vaccine candidates in experimental murine cysticercosis

Human cysticercosis is a public health problem caused by Taenia solium metacestodes; thus, eradication of T. solium transmission by vaccination is an urgent requirement. The Cc48 mimotope from T. solium cysticerci was tested expressed in phage particles (mCc48) and chemically synthesized (sCc48) as a vaccine candidate in experimental murine cysticercosis. For this, BALB/c mice were immunized with mCc48 (G1; n = 40), sCc48 (G2; n = 40) and phosphate-buffered saline (PBS) (G3; n = 40, positive control) and challenged with Taenia crassiceps metacestodes. Another PBS group without parasite challenge was used as a negative control (G4; n = 40). Mice were sacrificed 15, 30, 45 and 60 days post-infection for cysticerci and serum collection. Immunization efficacy was determined by cysticerci counting. Serum samples were tested by ELISA to verify antibody (IgM, IgG, IgA and IgE) and cytokine (IFNγ and IL-4) levels. The sCc48 achieved the highest rates of protection and efficacy (90 and 98%, respectively). The group immunized with mCc48 presented the highest reactivity for IgM, IgG and IgE. All groups presented IL-4, but IFNγ was quite variable among groups. The protection induced by sCc48 synthetic peptide supports further studies of this mimotope as a potential vaccine candidate against cysticercosis.

Arming Filamentous Bacteriophage, a Nature-Made Nanoparticle, for New Vaccine and Immunotherapeutic Strategies

The pharmaceutical use of bacteriophages as safe and inexpensive therapeutic tools is collecting renewed interest. The use of lytic phages to fight antibiotic-resistant bacterial strains is pursued in academic and industrial projects and is the object of several clinical trials. On the other hand, filamentous bacteriophages used for the phage display technology can also have diagnostic and therapeutic applications. Filamentous bacteriophages are nature-made nanoparticles useful for their size, the capability to enter blood vessels, and the capacity of high-density antigen expression. In the last decades, our laboratory focused its efforts in the study of antigen delivery strategies based on the filamentous bacteriophage 'fd', able to trigger all arms of the immune response, with particular emphasis on the ability of the MHC class I restricted antigenic determinants displayed on phages to induce strong and protective cytotoxic responses. We showed that fd bacteriophages, engineered to target mouse dendritic cells (DCs), activate innate and adaptive responses without the need of exogenous adjuvants, and more recently, we described the display of immunologically active lipids. In this review, we will provide an overview of the reported applications of the bacteriophage carriers and describe the advantages of exploiting this technology for delivery strategies.

Alternaria B Cell Mimotope Immunotherapy Alleviates Allergic Responses in a Mouse Model

Alternaria is a major outdoor allergen. Immunotherapy with Alternaria extracts has been documented to be effective in the sensitized patients. However, Alternaria extracts are notoriously difficult to standardize. Our aim is to screen the B cell mimotopes of Alternaria and to evaluate the therapeutic effects of B cell mimotope peptides on a BALB/c mouse model of Alternaria allergy. After a human sera pool from Alternaria monosensitized patients was established, B cell mimotopes were screened by a phage-displayed random heptamer peptide library that was identified via mixed Alternaria-specific IgE in the sera pool. B cell mimotopes with phage as a carrier were used to perform immunotherapy in an Alternaria allergy mouse model. Serological Ab levels, lung histology, and cytokine profiles were compared in the mimotope immunotherapy group, natural extract immunotherapy group, irrelevant phage control group, Alternaria-sensitized model group, and saline-blank group. Two mimotopes (MISTSRK and QKRNTIT) presented high binding ability with the sera of the Alternaria-allergic patients and mice and, therefore, were selected for immunotherapy in the mouse model. Compared with irrelevant phage control, model, and natural extract immunotherapy group, mimotope immunotherapy group significantly reduced serum IgE levels, inflammatory cells infiltration in the lung tissue, and IL-4 levels in bronchoalveolar lavage fluid, whereas serum IgG1 and IFN-γ levels in bronchoalveolar lavage fluid were increased. Our results indicate that B cell mimotopes of Alternaria alleviates allergic response in a mouse model and have potential as novel therapeutic agents for IgE-mediated Alternaria-allergic diseases.

Contribution of the Immune Response to Phage Therapy

Therapeutic phages are being employed for vaccination and treatment of cancer and bacterial infections. Their natural immunogenicity triggers intertwined interactions with innate and adaptive immune cells that might influence therapy. Phage- and bactierial-derived pathogen-associated molecular patterns released after bacterial lysis have been proposed to stimulate local innate immune responses, which could promote antitumor immunity or bacterial clearance. Conversely, immunogenicity of phages induces phage-specific humoral memory, which can hamper therapeutic success. This review outlines the current knowledge on the different types of immune responses elicited by phages and their potential benefits and adverse side effects, when applied therapeutically. This review further summarizes the knowledge gaps and defines the key immunological questions that need to be addressed regarding the clinical application of antibacterial phage therapy.

Phage proteins are expressed on the surface of Neisseria gonorrhoeae and are potential vaccine candidates

All Neisseria gonorrhoeae strains whose DNA sequences have been determined possess filamentous phage sequences representing their full genomes. The presence of filamentous phage DNA sequences in all sequenced N. gonorrhoeae strains suggest that purified phage particles might be used as a gonococcal vaccine. To test this hypothesis, we purified filamentous NgoΦfil phages and immunized rabbits subcutaneously. The elicited sera contained large quantities of anti-phage IgG and IgA antibodies that bound to the surface of N. gonorrhoeae cells, as shown by ELISA and flow cytometry. The elicited sera bound to the structural NgoΦ6fil proteins present in phage particles and to N. gonorrhoeae cells. The sera did not react with gonococcal outer membrane proteins. The sera also had bactericidal activity and blocked adhesion of gonococci to tissue culture cells. These data demonstrate that NgoΦfil phage particles can induce antibodies with anti-gonococcal activity and may be a candidate for vaccine development.

Vectorized Delivery of Alpha-GalactosylCeramide and Tumor Antigen on Filamentous Bacteriophage fd Induces Protective Immunity by Enhancing Tumor-Specific T Cell Response

We have exploited the properties of filamentous bacteriophage fd to deliver immunologically active lipids together with antigenic peptides. Filamentous bacteriophages resemble for size, capability to be permeable to blood vessels, and high density antigen expression, a nature-made nanoparticle. In addition, their major coat protein pVIII, which is arranged to form a tubular shield surrounding the phage genome, has a high content of hydrophobic residues promoting lipid association. We conjugated bacteriophages to alpha-GalactosylCeramide (α-GalCer), a lipid antigen-stimulating invariant natural killer T (iNKT) cells and capable of inducing their anti-tumoral activities. We found that bacteriophage fd/α-GalCer conjugates could repeatedly stimulate iNKT cells in vitro and in vivo, without inducing iNKT anergy. Moreover, co-delivery of α-GalCer and a MHC class I restricted tumor-associated antigenic determinant to antigen-presenting cells via bacteriophages strongly boosted adaptive CD8⁺ T cell response and efficiently delayed tumor progression. Co-delivery of a tumor antigen and iNKT-stimulatory lipid on the surface of filamentous bacteriophages is a novel approach to potentiate adaptive anti-cancer immune responses, overcoming the current limitations in the use of free α-GalCer and may represent an attractive alternative to existing delivery methods, opening the path to a potential translational usage of this safe, inexpensive, and versatile tool.

Immunocontraception: Filamentous Bacteriophage as a Platform for Vaccine Development

BACKGROUND

Population control of domestic, wild, invasive, and captive animal species is a global issue of importance to public health, animal welfare and the economy. There is pressing need for effective, safe, and inexpensive contraceptive technologies to address this problem. Contraceptive vaccines, designed to stimulate the immune system in order to block critical reproductive events and suppress fertility, may provide a solution. Filamentous bacteriophages can be used as platforms for development of such vaccines.

OBJECTIVE

In this review authors highlight structural and immunogenic properties of filamentous phages, and discuss applications of phage-peptide vaccines for advancement of immunocontraception technology in animals.

RESULTS

Phages can be engineered to display fusion (non-phage) peptides as coat proteins. Such modifications can be accomplished via genetic manipulation of phage DNA, or by chemical conjugation of synthetic peptides to phage surface proteins. Phage fusions with antigenic determinants induce humoral as well as cell-mediated immune responses in animals, making them attractive as vaccines. Additional advantages of the phage platform include environmental stability, low cost, and safety for immunized animals and those administering the vaccines.

CONCLUSION

Filamentous phages are viable platforms for vaccine development that can be engineered with molecular and organismal specificity. Phage-based vaccines can be produced in abundance at low cost, are environmentally stable, and are immunogenic when administered via multiple routes. These features are essential for a contraceptive vaccine to be operationally practical in animal applications. Adaptability of the phage platform also makes it attractive for design of human immunocontraceptive agents.

Real-Time qPCR as a Method for Detection of Antibody-Neutralized Phage Particles

The most common method for phage quantitation is the plaque assay, which relies on phage ability to infect bacteria. However, non-infective phage particles may preserve other biological properties; specifically, they may enter interactions with the immune system of animals and humans. Here, we demonstrate real-time quantitative polymerase chain reaction (qPCR) detection of bacteriophages as an alternative to the plaque assay. The closely related staphylococcal bacteriophages A3R and 676Z and the coliphage T4 were used as model phages. They were tested in vivo in mice, ex vivo in human sera, and on plastic surfaces designed for ELISAs. T4 phage was injected intravenously into pre-immunized mice. The phage was completely neutralized by specific antibodies within 5 h (0 pfu/ml of serum, as determined by the plaque assay), but it was still detected by qPCR in the amount of approximately 10⁷ pfu/ml of serum. This demonstrates a substantial timelapse between "microbiological disappearance" and true clearance of phage particles from the circulation. In human sera ex vivo, qPCR was also able to detect neutralized phage particles that were not detected by the standard plaque assay. The investigated bacteriophages differed considerably in their ability to immobilize on plastic surfaces: this difference was greater than one order of magnitude, as shown by qPCR of phage recovered from plastic plates. The ELISA did not detect differences in phage binding to plates. Major limitations of qPCR are possible inhibitors of the PCR reaction or free phage DNA, which need to be considered in procedures of phage sample preparation for qPCR testing. We propose that phage pharmacokinetic and pharmacodynamic studies should not rely merely on detection of antibacterial activity of a phage. Real-time qPCR can be an alternative for phage detection, especially in immunological studies of bacteriophages. It can also be useful for studies of phage-based drug nanocarriers or biosensors.

Injected phage-displayed-VP28 vaccine reduces shrimp Litopenaeus vannamei mortality by white spot syndrome virus infection

White spot syndrome virus (WSSV) is the most important viral pathogen for the global shrimp industry causing mass mortalities with huge economic losses. Recombinant phages are capable of expressing foreign peptides on viral coat surface and act as antigenic peptide carriers bearing a phage-displayed vaccine. In this study, the full-length VP28 protein of WSSV, widely known as potential vaccine against infection in shrimp, was successfully cloned and expressed on M13 filamentous phage. The functionality and efficacy of this vaccine immunogen was demonstrated through immunoassay and in vivo challenge studies. In ELISA assay phage-displayed VP28 was bind to Litopenaeus vannamei immobilized hemocyte in contrast to wild-type M13 phage. Shrimps were injected with 2 × 10(10) cfu animal(-1) single dose of VP28-M13 and M13 once and 48 h later intramuscularly challenged with WSSV to test the efficacy of the vaccine against the infection. All dead challenged shrimps were PCR WSSV-positive. The accumulative mortality of the vaccinated and challenged shrimp groups was significantly lower (36.67%) than the unvaccinated group (66.67%). Individual phenoloxidase and superoxide dismutase activity was assayed on 8 and 48 h post-vaccination. No significant difference was found in those immunological parameters among groups at any sampled time evaluated. For the first time, phage display technology was used to express a recombinant vaccine for shrimp. The highest percentage of relative survival in vaccinated shrimp (RPS = 44.99%) suggest that the recombinant phage can be used successfully to display and deliver VP28 for farmed marine crustaceans.

Oral Immunization of Rabbits with S. enterica Typhimurium Expressing Neisseria gonorrhoeae Filamentous Phage Φ6 Induces Bactericidal Antibodies Against N. gonorrhoeae

All Neisseria gonorrhoeae strains whose DNA sequences have been determined possess filamentous phage DNA sequences. To ascertain if phage encoded proteins could form the basis of a gonococcal vaccine, rabbits were orally infected with S. entericaTyphimurium strain χ3987 harboring phagemid NgoΦ6 fm. The elicited sera contained large quantities of anti-phage IgG and IgA antibodies that bound to the surface of N. gonorrhoeae cells, as shown by indirect fluorescent analysis and flow cytometry. The elicited sera was able to bind to several phage proteins. The sera also had bactericidal activity. These data demonstrate that N. gonorrhoeae filamentous phage can induce antibodies with anti-gonococcal activity and that phage proteins may be a candidate for vaccine development.

Humoral immune responses against gonadotropin releasing hormone elicited by immunization with phage-peptide constructs obtained via phage display

Phage display is based on genetic engineering of phage coat proteins resulting in fusion peptides displayed on the surface of phage particles. The technology is widely used for generation of phages with novel characteristics for numerous applications in biomedicine and far beyond. The focus of this study was on development of phage-peptide constructs that stimulate production of antibodies against gonadotropin releasing hormone (GnRH). Phage-peptide constructs that elicit production of neutralizing GnRH antibodies can be used for anti-fertility and anti-cancer applications. Phage-GnRH constructs were generated via selection from a phage display library using several types of GnRH antibodies as selection targets. Such phage constructs were characterized for sequence similarities to GnRH peptide and frequency of their occurrence in the selection rounds. Five of the constructs with suitable characteristics were tested in mice as a single dose 5×10(11) virions (vir) vaccine and were found to be able to stimulate production of GnRH-specific antibodies, but not to suppress testosterone (indirect indicator of GnRH antibody neutralizing properties). Next, one of the constructs was tested at a higher dose of 2×10(12) vir per mouse in combination with a poly(lactide-co-glycolide) (PLGA)-based adjuvant. This resulted in multifold increase in GnRH antibody production and significant reduction of serum testosterone, indicating that antibodies produced in response to the phage-GnRH immunization possess neutralizing properties. To achieve optimal immune responses for desired applications, phage-GnRH constructs can be modified with respect to flanking sequences of GnRH-like peptides displayed on phage. Anticipated therapeutic effects also might be attained using optimized phage doses, a combination of several constructs in a single treatment, or application of adjuvants and advanced phage delivery systems.

Beyond phage display: non-traditional applications of the filamentous bacteriophage as a vaccine carrier, therapeutic biologic, and bioconjugation scaffold

For the past 25 years, phage display technology has been an invaluable tool for studies of protein-protein interactions. However, the inherent biological, biochemical, and biophysical properties of filamentous bacteriophage, as well as the ease of its genetic manipulation, also make it an attractive platform outside the traditional phage display canon. This review will focus on the unique properties of the filamentous bacteriophage and highlight its diverse applications in current research. Particular emphases are placed on: (i) the advantages of the phage as a vaccine carrier, including its high immunogenicity, relative antigenic simplicity and ability to activate a range of immune responses, (ii) the phage's potential as a prophylactic and therapeutic agent for infectious and chronic diseases, (iii) the regularity of the virion major coat protein lattice, which enables a variety of bioconjugation and surface chemistry applications, particularly in nanomaterials, and (iv) the phage's large population sizes and fast generation times, which make it an excellent model system for directed protein evolution. Despite their ubiquity in the biosphere, metagenomics work is just beginning to explore the ecology of filamentous and non-filamentous phage, and their role in the evolution of bacterial populations. Thus, the filamentous phage represents a robust, inexpensive, and versatile microorganism whose bioengineering applications continue to expand in new directions, although its limitations in some spheres impose obstacles to its widespread adoption and use.

Phage display as a technology delivering on the promise of peptide drug discovery

Phage display represents an important approach in the development pipeline for producing peptides and peptidomimetics therapeutics. Using randomly generated DNA sequences and molecular biology techniques, large diverse peptide libraries can be displayed on the phage surface. The phage library can be incubated with a target of interest and the phage which bind can be isolated and sequenced to reveal the displayed peptides' primary structure. In this review, we focus on the 'mechanics' of the phage display process, whilst highlighting many diverse and subtle ways it has been used to further the drug-development process, including the potential for the phage particle itself to be used as a drug carrier targeted to a particular pathogen or cell type in the body.

Identification and characterization of a peptide affinity reagent for detection of noroviruses in clinical samples

Norovirus (NoV) is the most common agent of nonbacterial epidemic gastroenteritis and is estimated to cause 21 million cases of the disease in the United States annually. The antigen enzyme-linked immunosorbent assays (ELISAs) currently available for NoV diagnosis detect only certain strains and are approved for use in the United States only in epidemics where NoV is suspected. There is a clear need for simpler, more rapid, and more reliable diagnostic tools for the detection of NoV. In this study, phage display technology was used to screen a library of phage displaying random 12-mer peptides for those that bind to Norwalk virus virus-like particles (NV VLPs). Three phage clones displaying unique peptides were identified, and both the peptide-displaying phages and the peptides were confirmed to bind specifically to NV VLPs. The peptide displayed on phage clone NV-N-R5-1 was determined to bind to the protruding domain of the VP1 capsid protein. This phage also bound to NV VLPs seeded into NoV-negative stool with a limit of detection of 1.56 ng NV VLP. This value was comparable to monoclonal antibody (MAb) 3912, which is currently used in commercially available assays. Furthermore, the NV-N-R5-1 phage exhibited high specificity by detecting NV only in previously characterized NV-positive stool samples in contrast to no detection in NV-negative stool samples. These data demonstrate that the further development of NV-N-R5-1 phage as a diagnostic reagent is possible and might offer several distinct advantages over antibodies, such as decreases in the time and cost of production and ease of isolating phage against other epidemic strains currently circulating as well as those that are emerging.